Wetlands are known to be the most biologically productive ecosystems in the temperate regions of the earth. Their biological productivity rivals that of tropical rainforests and involves complex nutrient and energy cycles. Many wetland functions are a direct result of the biological activity that occurs in wetlands.
Fish and Wildlife Habitat
Fish and wildlife habitat is the most widely celebrated and actively enjoyed wetland function. In fact, it was this particular function that first inspired individuals and organizations like Ducks Unlimited and the Audubon Society to promote wetland protection in the early part of the 20th century. Some species spend their entire lives in wetlands, while others utilize them intermittently for feeding or rearing their young. Simply put, wetlands provide critical habitat for Michigan's wildlife.
Most freshwater fish are considered wetland dependent. Fish feed in wetlands or on food produced there. Wetlands serve as nursery grounds for many species whose young take cover there, and many important sport fishes spawn in or near wetlands.
Like fish, many bird species are dependent on wetlands for either migratory resting places, breeding or feeding grounds, or cover from predators. It is estimated that more than one-third of all bird species in North America rely on wetlands for at least one of these purposes.
Nearly all of Michigan's amphibians are wetland dependent, especially for breeding. Amphibians are sensitive to changes in wetland quality and quantity. Many scientists correlate declines in amphibian populations with wetland degradation worldwide.
Wetlands serve as the preferred habitat for many mammals such as muskrat, beaver, otter, mink, and raccoon. In Northern Michigan, cedar swamps are critical to white-tailed deer for many reasons, including winter browse (northern white cedar sustains deer in the absence of other foods) and important thermal cover during harsh winters.
Threatened and Endangered Species Habitat
Wetland habitats are critical for the survival of threatened or endangered species. Endangered species are those that are in danger of becoming extinct. Threatened species are those that are in danger of becoming endangered. These species represent a unique element of Michigan's valuable natural heritage. More than one-third of all threatened or endangered animal species in the United States live in wetland areas or depend on wetlands for some part of their life cycle. This is especially critical considering that wetlands comprise only about five percent of the lower 48 United States.
Examples of Michigan's threatened or endangered animals that rely on wetlands include the bald eagle, osprey, common loon, and king rail. According to the Michigan Natural features inventory, of Michigan's total 395 threatened, endangered, rare, and special concern plant species, 194 of them are found in wetland habitats. Thus, nearly 50% of Michigan's plants of management concern reside in less than 15% percent of Michigan's surface area.
Water Pollution Control
A major function of wetlands is the preservation of water quality. In a sense, wetlands function like living filters by trapping polluting nutrients and sediments from surface and ground water.
Although less well-known than providing fish and wildlife habitat, this wetland function is important to the integrity of aquatic ecosystems and can influence all other functions. Excess inputs of nutrients such as phosphorus and nitrogen can cause severe problems in aquatic ecosystems. You might say, "But I thought nutrients were good?" Nutrients such as phosphorus are necessary, but can be a classic example of how "too much of a good thing is bad."
Excess nutrients can cause an undesirable increase in algae and aquatic plant growth. The result is water that is reminiscent of pea soup, weed-choked lakes, depleted dissolved oxygen levels, and the rapid aging or "eutrophication" of a lake. This in turn impacts other functions such as use for recreation and fish and wildlife habitat.
In the Great Lakes Region, the massive algae blooms and depleted dissolved oxygen levels of Lake Erie in the early 1970s is a classic example of what happens to an aquatic system under the strain of too many nutrients. Wetlands retain or remove nutrients in four ways: 1) uptake by plant life, 2) adsorption into sediments, 3) deposition of detritus (organic materials), and 4) chemical precipitation. The most significant of these is the uptake of nutrients by plants (which occurs primarily during the growing season, the same time that lakes and streams are most sensitive to nutrient inputs) and adsorption into sediments.
As sediment-laden water flows through a wetland from the surrounding watershed, the sediments are deposited in the wetland. This reduces siltation into lakes, rivers, and streams. A combination of wetland vegetation and generally flat topography serves to slow water flow and increase deposition of silt and organic matter (carbon compounds). Because of the soil chemistry in wetlands, carbon compounds that are deposited in wetlands decompose very slowly. In this manner, wetlands serve as a relatively permanent resting place for carbon compounds. This function of wetlands can help to trap carbon that would otherwise accumulate in the upper atmosphere and contribute to global climate change. Furthermore, there is a strong tendency for heavy metals and other toxic chemicals to attach to the sediment particles found in surface water runoff. Wetlands can trap these human-induced pollutants and remove them from the water column. However, when the natural ability of a wetland to function as a filter is overstressed from human inputs, the wetland and its functions can be destroyed. In fact, when overloaded, wetlands can actually become sources of pollutants, exporting materials that have been filtered and stored for centuries.
Barrier to Waves and Erosion
In their natural condition, wetlands function as a barrier to erosion along shorelines. The root systems of wetland plants stabilize soil at the water's edge and enhance soil accumulation at the shoreline. Wetland vegetation along shorelines reduces erosion by dampening wave action and slowing current speed.
Wetlands are usually found where the ground water table intersects or is close to the land surface. They are usually sites of springs or seeps where ground water is discharged and are very important for providing high quality water for our lakes and streams. However, some wetlands are found where ground water seeps back into the earth and recharges aquifers. The recharge potential of a wetland varies according to a variety of factors, including wetland type, geographic location, subsurface geology, soil type, and precipitation.
Flood Storage and Conveyance
Wetlands act as a hydrologic sponge, temporarily storing flood waters and releasing them slowly, thus reducing flood peaks and protecting downstream property owners from flood damage. Wetlands and adjacent floodplains often form natural floodways that convey flood waters from upland to downstream points. These functions become increasingly important in urban areas where development has increased the rate and volume of runoff.